.\"$Id: tcpflow.1.in,v 1.5 2001/02/26 23:01:30 jelson Exp $"
.TH tcpflow 1 "20 April 1999" "tcpflow @VERSION@" "tcpflow @VERSION@"
.SH NAME
tcpflow \- TCP flow recorder 
.SH SYNOPSIS
.na
.B tcpflow
[\c
.BI \-chpsv\fR\c
]
[\c
.BI \-b \ max_bytes\fR\c
]
[\c
.BI \-d \ debug_level\fR\c
]
[\c
.BI \-f \ max_fds\fR\c
]
[\c
.BI \-i \ iface\fR\c
]
[\c
.BI \-r \ file\fR\c
]
[\c
.BI expression\fR\c
]
.SH DESCRIPTION
.LP
.B tcpflow
is a program that captures data transmitted as part of TCP connections
(flows), and stores the data in a way that is convenient for protocol
analysis or debugging.  A program like
.IR tcpdump(4)
shows a summary of packets seen on the wire, but usually doesn't store
the data that's actually being transmitted.  In contrast, tcpflow
reconstructs the actual data streams and stores each flow in a
separate file for later analysis.  tcpflow understands TCP sequence
numbers and will correctly reconstruct data streams regardless of
retransmissions or out-of-order delivery.
.LP
tcpflow stores all captured data in files that have names of the form
.in +.5i
.nf
192.168.101.102.02345-010.011.012.013.45103
.fi
.in -.5i
where the contents of the above file would be data transmitted from
host 192.168.101.102 port 2345, to host 10.11.12.13 port 45103.
.SH OPTIONS
.TP
.B \-b
Max bytes per flow.  Capture no more than \fImax_bytes\fP bytes per
flow.  Any data captured for a flow beyond \fImax_bytes\fP from the
first byte captured will be discarded.  The default is to store an
unlimited number of bytes per flow.
.TP
.B \-c
Console print.  Print the contents of packets to stdout as they
are received, without storing any captured data to files (implies
.B -s
).
.TP
.B \-d
Debug level.  Set the level of debugging messages printed to stderr to
\fIdebug_level\fP.  Higher numbers produce more messages.
.B \-d 0
causes completely silent operation.
.B \-d 1
, the default, produces minimal status messages.
.B \-d 10
produces verbose output equivalent to
.B \-v .
Numbers higher than 10 can produce a large
amount of debugging information useful only to developers.
.TP
.B \-f
Max file descriptors used.  Limit the number of file descriptors used
by tcpflow to \fImax_fds\fP.  Higher numbers use more system
resources, but usually perform better.  If the underlying operating
system supports the
.B setrlimit()
system call, the OS will be asked to enforce the requested limit.  The
default is for tcpflow to use the maximum number of file descriptors
allowed by the OS.  The
.B \-v
option will report how many file descriptors tcpflow is using.
.TP
.B \-h
Help.  Print usage information and exit.
.TP
.B \-i
Interface name.  Capture packets from the network interface
named \fIiface\fP.  If no interface is specified with
.B \-i
, a reasonable default will be used by libpcap automatically.
.TP
.B \-p
No promiscuous mode.  Normally, tcpflow attempts to put the network
interface into promiscuous mode before capturing packets.  The
.B \-p
option tells tcpflow
.B not
to put the interface into promiscuous mode.  Note that it might
already be in promiscuous mode for some other reason.
.TP
.B \-r
Read from file.  Read packets from \fIfile\fP, which was created using the
.B \-w
option of
.IR tcpdump (1).
Standard input is used if \fIfile\fP is ``-''.
Note that for this option to be useful, tcpdump's
.B \-s
option should be used to set the snaplen to the MTU of the interface
(e.g., 1500) while capturing packets.
.TP
.B \-s
Strip non-printables.  Convert all non-printable characters to the
"." character before printing packets to the console or storing them
to a file.
.TP
.B \-v
Verbose operation.  Verbosely describe tcpflow's operation.
Equivalent to
.B \-d 10 .
.\"START -- tcpdump excerpt"
.SH FILTERING EXPRESSIONS
The
.B expression
specified on the command-line specifies which packets should be
captured.  Because tcpflow uses the the libpcap library, tcpflow has
the same powerful filtering language available as programs such as
.IR tcpdump (1).
.LP
.B The following part of the man page is excerpted from the tcpdump man page.
.LP

\fIexpression\fP selects which packets will be dumped.  If no
\fIexpression\fP is given, all packets on the net will be dumped.
Otherwise, only packets for which \fIexpression\fP is `true' will be
dumped.
.LP
The \fIexpression\fP consists of one or more
.I primitives.
Primitives usually consist of an
.I id
(name or number) preceded by one or more qualifiers.  There are three
different kinds of qualifier:
.IP \fItype\fP
qualifiers say what kind of thing the id name or number refers to.
Possible types are
.BR host ,
.B net
and
.BR port .
E.g., `host foo', `net 128.3', `port 20'.  If there is no type
qualifier,
.B host
is assumed.
.IP \fIdir\fP
qualifiers specify a particular transfer direction to and/or from
.I id.
Possible directions are
.BR src ,
.BR dst ,
.B "src or dst"
and
.B "src and"
.BR dst .
E.g., `src foo', `dst net 128.3', `src or dst port ftp-data'.  If
there is no dir qualifier,
.B "src or dst"
is assumed.
For `null' link layers (i.e. point to point protocols such as slip) the
.B inbound
and
.B outbound
qualifiers can be used to specify a desired direction.
.IP \fIproto\fP
qualifiers restrict the match to a particular protocol.  Possible
protos are:
.BR ether ,
.BR fddi ,
.BR ip ,
.BR arp ,
.BR rarp ,
.BR decnet ,
.BR lat ,
.BR sca ,
.BR moprc ,
.BR mopdl ,
.B tcp
and
.BR udp .
E.g., `ether src foo', `arp net 128.3', `tcp port 21'.  If there is
no proto qualifier, all protocols consistent with the type are
assumed.  E.g., `src foo' means `(ip or arp or rarp) src foo'
(except the latter is not legal syntax), `net bar' means `(ip or
arp or rarp) net bar' and `port 53' means `(tcp or udp) port 53'.
.LP
[`fddi' is actually an alias for `ether'; the parser treats them
identically as meaning ``the data link level used on the specified
network interface.''  FDDI headers contain Ethernet-like source
and destination addresses, and often contain Ethernet-like packet
types, so you can filter on these FDDI fields just as with the
analogous Ethernet fields.  FDDI headers also contain other fields,
but you cannot name them explicitly in a filter expression.]
.LP
In addition to the above, there are some special `primitive' keywords
that don't follow the pattern:
.BR gateway ,
.BR broadcast ,
.BR less ,
.B greater
and arithmetic expressions.  All of these are described below.
.LP
More complex filter expressions are built up by using the words
.BR and ,
.B or
and
.B not
to combine primitives.  E.g., `host foo and not port ftp and not port ftp-data'.
To save typing, identical qualifier lists can be omitted.  E.g.,
`tcp dst port ftp or ftp-data or domain' is exactly the same as
`tcp dst port ftp or tcp dst port ftp-data or tcp dst port domain'.
.LP
Allowable primitives are:
.IP "\fBdst host \fIhost\fR"
True if the IP destination field of the packet is \fIhost\fP,
which may be either an address or a name.
.IP "\fBsrc host \fIhost\fR"
True if the IP source field of the packet is \fIhost\fP.
.IP "\fBhost \fIhost\fP
True if either the IP source or destination of the packet is \fIhost\fP.
Any of the above host expressions can be prepended with the keywords,
\fBip\fP, \fBarp\fP, or \fBrarp\fP as in:
.in +.5i
.nf
\fBip host \fIhost\fR
.fi
.in -.5i
which is equivalent to:
.in +.5i
.nf
\fBether proto \fI\\ip\fB and host \fIhost\fR
.fi
.in -.5i
If \fIhost\fR is a name with multiple IP addresses, each address will
be checked for a match.
.IP "\fBether dst \fIehost\fP
True if the ethernet destination address is \fIehost\fP.  \fIEhost\fP
may be either a name from /etc/ethers or a number (see
.IR ethers (3N)
for numeric format).
.IP "\fBether src \fIehost\fP
True if the ethernet source address is \fIehost\fP.
.IP "\fBether host \fIehost\fP
True if either the ethernet source or destination address is \fIehost\fP.
.IP "\fBgateway\fP \fIhost\fP
True if the packet used \fIhost\fP as a gateway.  I.e., the ethernet
source or destination address was \fIhost\fP but neither the IP source
nor the IP destination was \fIhost\fP.  \fIHost\fP must be a name and
must be found in both /etc/hosts and /etc/ethers.  (An equivalent
expression is
.in +.5i
.nf
\fBether host \fIehost \fBand not host \fIhost\fR
.fi
.in -.5i
which can be used with either names or numbers for \fIhost / ehost\fP.)
.IP "\fBdst net \fInet\fR"
True if the IP destination address of the packet has a network
number of \fInet\fP. \fINet\fP may be either a name from /etc/networks
or a network number (see \fInetworks(5)\fP for details).
.IP "\fBsrc net \fInet\fR"
True if the IP source address of the packet has a network
number of \fInet\fP.
.IP "\fBnet \fInet\fR"
True if either the IP source or destination address of the packet has a network
number of \fInet\fP.
.IP "\fBnet \fInet\fR \fBmask \fImask\fR"
True if the IP address matches \fInet\fR with the specific netmask.
May be qualified with \fBsrc\fR or \fBdst\fR.
.IP "\fBnet \fInet\fR/\fIlen\fR"
True if the IP address matches \fInet\fR a netmask \fIlen\fR bits wide.
May be qualified with \fBsrc\fR or \fBdst\fR.
.IP "\fBdst port \fIport\fR"
True if the packet is ip/tcp or ip/udp and has a
destination port value of \fIport\fP.
The \fIport\fP can be a number or a name used in /etc/services (see
.IR tcp (4P)
and
.IR udp (4P)).
If a name is used, both the port
number and protocol are checked.  If a number or ambiguous name is used,
only the port number is checked (e.g., \fBdst port 513\fR will print both
tcp/login traffic and udp/who traffic, and \fBport domain\fR will print
both tcp/domain and udp/domain traffic).
.IP "\fBsrc port \fIport\fR"
True if the packet has a source port value of \fIport\fP.
.IP "\fBport \fIport\fR"
True if either the source or destination port of the packet is \fIport\fP.
Any of the above port expressions can be prepended with the keywords,
\fBtcp\fP or \fBudp\fP, as in:
.in +.5i
.nf
\fBtcp src port \fIport\fR
.fi
.in -.5i
which matches only tcp packets whose source port is \fIport\fP.
.IP "\fBless \fIlength\fR"
True if the packet has a length less than or equal to \fIlength\fP.
This is equivalent to:
.in +.5i
.nf
\fBlen <= \fIlength\fP.
.fi
.in -.5i
.IP "\fBgreater \fIlength\fR"
True if the packet has a length greater than or equal to \fIlength\fP.
This is equivalent to:
.in +.5i
.nf
\fBlen >= \fIlength\fP.
.fi
.in -.5i
.IP "\fBip proto \fIprotocol\fR"
True if the packet is an ip packet (see
.IR ip (4P))
of protocol type \fIprotocol\fP.
\fIProtocol\fP can be a number or one of the names
\fIicmp\fP, \fIigrp\fP, \fIudp\fP, \fInd\fP, or \fItcp\fP.
Note that the identifiers \fItcp\fP, \fIudp\fP, and \fIicmp\fP are also
keywords and must be escaped via backslash (\\), which is \\\\ in the C-shell.
.IP "\fBether broadcast\fR"
True if the packet is an ethernet broadcast packet.  The \fIether\fP
keyword is optional.
.IP "\fBip broadcast\fR"
True if the packet is an IP broadcast packet.  It checks for both
the all-zeroes and all-ones broadcast conventions, and looks up
the local subnet mask.
.IP "\fBether multicast\fR"
True if the packet is an ethernet multicast packet.  The \fIether\fP
keyword is optional.
This is shorthand for `\fBether[0] & 1 != 0\fP'.
.IP "\fBip multicast\fR"
True if the packet is an IP multicast packet.
.IP  "\fBether proto \fIprotocol\fR"
True if the packet is of ether type \fIprotocol\fR.
\fIProtocol\fP can be a number or a name like
\fIip\fP, \fIarp\fP, or \fIrarp\fP.
Note these identifiers are also keywords
and must be escaped via backslash (\\).
[In the case of FDDI (e.g., `\fBfddi protocol arp\fR'), the
protocol identification comes from the 802.2 Logical Link Control
(LLC) header, which is usually layered on top of the FDDI header.
\fITcpdump\fP assumes, when filtering on the protocol identifier,
that all FDDI packets include an LLC header, and that the LLC header
is in so-called SNAP format.]
.IP "\fBdecnet src \fIhost\fR"
True if the DECNET source address is
.IR host ,
which may be an address of the form ``10.123'', or a DECNET host
name.  [DECNET host name support is only available on Ultrix systems
that are configured to run DECNET.]
.IP "\fBdecnet dst \fIhost\fR"
True if the DECNET destination address is
.IR host .
.IP "\fBdecnet host \fIhost\fR"
True if either the DECNET source or destination address is
.IR host .
.IP "\fBip\fR, \fBarp\fR, \fBrarp\fR, \fBdecnet\fR"
Abbreviations for:
.in +.5i
.nf
\fBether proto \fIp\fR
.fi
.in -.5i
where \fIp\fR is one of the above protocols.
.IP "\fBlat\fR, \fBmoprc\fR, \fBmopdl\fR"
Abbreviations for:
.in +.5i
.nf
\fBether proto \fIp\fR
.fi
.in -.5i
where \fIp\fR is one of the above protocols.
Note that
\fItcpdump\fP does not currently know how to parse these protocols.
.IP  "\fBtcp\fR, \fBudp\fR, \fBicmp\fR"
Abbreviations for:
.in +.5i
.nf
\fBip proto \fIp\fR
.fi
.in -.5i
where \fIp\fR is one of the above protocols.
.IP  "\fIexpr relop expr\fR"
True if the relation holds, where \fIrelop\fR is one of >, <, >=, <=, =, !=,
and \fIexpr\fR is an arithmetic expression composed of integer constants
(expressed in standard C syntax), the normal binary operators
[+, -, *, /, &, |], a length operator, and special packet data accessors.
To access
data inside the packet, use the following syntax:
.in +.5i
.nf
\fIproto\fB [ \fIexpr\fB : \fIsize\fB ]\fR
.fi
.in -.5i
\fIProto\fR is one of \fBether, fddi,
ip, arp, rarp, tcp, udp, \fRor \fBicmp\fR, and
indicates the protocol layer for the index operation.
The byte offset, relative to the indicated protocol layer, is
given by \fIexpr\fR.
\fISize\fR is optional and indicates the number of bytes in the
field of interest; it can be either one, two, or four, and defaults to one.
The length operator, indicated by the keyword \fBlen\fP, gives the
length of the packet.

For example, `\fBether[0] & 1 != 0\fP' catches all multicast traffic.
The expression `\fBip[0] & 0xf != 5\fP'
catches all IP packets with options. The expression
`\fBip[6:2] & 0x1fff = 0\fP'
catches only unfragmented datagrams and frag zero of fragmented datagrams.
This check is implicitly applied to the \fBtcp\fP and \fBudp\fP
index operations.
For instance, \fBtcp[0]\fP always means the first
byte of the TCP \fIheader\fP, and never means the first byte of an
intervening fragment.
.LP
Primitives may be combined using:
.IP
A parenthesized group of primitives and operators
(parentheses are special to the Shell and must be escaped).
.IP
Negation (`\fB!\fP' or `\fBnot\fP').
.IP
Concatenation (`\fB&&\fP' or `\fBand\fP').
.IP
Alternation (`\fB||\fP' or `\fBor\fP').
.LP
Negation has highest precedence.
Alternation and concatenation have equal precedence and associate
left to right.  Note that explicit \fBand\fR tokens, not juxtaposition,
are now required for concatenation.
.LP
If an identifier is given without a keyword, the most recent keyword
is assumed.
For example,
.in +.5i
.nf
\fBnot host vs and ace\fR
.fi
.in -.5i
is short for
.in +.5i
.nf
\fBnot host vs and host ace\fR
.fi
.in -.5i
which should not be confused with
.in +.5i
.nf
\fBnot ( host vs or ace )\fR
.fi
.in -.5i
.LP
Expression arguments can be passed to tcpdump as either a single argument
or as multiple arguments, whichever is more convenient.
Generally, if the expression contains Shell metacharacters, it is
easier to pass it as a single, quoted argument.
Multiple arguments are concatenated with spaces before being parsed.
.SH EXAMPLES
.LP
.B The following part of the man page is excerpted from the tcpdump man page.
.LP
To record all packets arriving at or departing from \fIsundown\fP:
.RS
.nf
\fBtcpflow host sundown\fP
.fi
.RE
.LP
To record traffic between \fIhelios\fR and either \fIhot\fR or \fIace\fR:
.RS
.nf
\fBtcpflow host helios and \\( hot or ace \\)\fP
.fi
.RE
.LP
To record traffic between \fIace\fR and any host except \fIhelios\fR:
.RS
.nf
\fBtcpflow host ace and not helios\fP
.fi
.RE
.LP
To record all traffic between local hosts and hosts at Berkeley:
.RS
.nf
.B
tcpflow net ucb-ether
.fi
.RE
.LP
To record all ftp traffic through internet gateway \fIsnup\fP:
(note that the expression is quoted to prevent the shell from
(mis-)interpreting the parentheses):
.RS
.nf
.B
tcpflow 'gateway snup and (port ftp or ftp-data)'
.fi
.RE
.LP
.\"END -- tcpdump excerpt"
.SH BUGS
Please send bug reports to jelson@circlemud.org.
.LP
tcpflow currently does not understand IP fragments.  Flows containing
IP fragments will not be recorded correctly.
.LP
tcpflow never frees state associated with flows that it records, so
will grow large if used to capture a very large number of flows (e.g.,
on the order of 100,000 flows or more).
.LP
There appears to be a bug in the way that Linux delivers packets to
libpcap when using the loopback interface ("localhost").  When
listening to the Linux loopback interface, selective packet filtering
is not possible; all TCP flows on the localhost interface will be
recorded.
.SH AUTHOR
Jeremy Elson <jelson@circlemud.org>
.LP
The current version of this software is available at
.RS
.I http://www.circlemud.org/~jelson/software/tcpflow
.RE
.SH "SEE ALSO"
tcpdump(1), nit(4P), bpf(4), pcap(3)
